Materials such as plastics are frequently molded into desired shapes through the use of injection molding equipment having an injection unit and a clamping unit. In a conventional injection molding process, a pellet or powder resin is melted within a heating chamber of the injection unit. The injection unit further includes a hydraulic piston or ram which pushes the melted plastic past a "torpedo" or spreader that spreads the melted plastic. This enables improved thermal contact with the heating chamber and thus improves the flow of the melted plastic. The melted plastic then converges at a nozzle which is connected to a sprue located within the mold. The sprue is connected to a gate by a runner that is formed in the mold through which the melted plastic flows. The gate serves to direct the flow of melted plastic into a mold cavity to thus form a desired part. Additionally, the gate limits backflow of the melted plastic. Further, the clamping unit provides a clamping force to hold the mold together during the injection molding process. In a mold type known as a cold runner mold, the melted plastic left in the runner is allowed to cool and solidify. This material is then later separated from the part and may be recycled for later use.
Projection televisions, such as rear projection televisions, typically include relatively large and/or asymmetric parts which are fabricated using injection molding techniques. Referring to FIG. 1, a front portion 12 and a rear mirror cover 14 of a rear projection television 10 fabricated by an injection molding process are shown. It is noted that the front portion 12 may be either a cabinet or a beznet. A mirror 16 is used in such televisions for reflecting an image onto a screen. The mirror 16 includes a first reflection surface 18 and a mounting surface 20. The mirror cover 14 includes an inner surface 22 having first 24, second 26, third 28 and fourth 30 mirror mounting areas which may include either mounting blocks or bosses. The mounting areas 24,26,28,30 are positioned in an upper area of the inner surface 22. In use, the mounting surface 20 is positioned upon the mounting areas 24,26,28,30. Upper 32 and lower 34 mirror holders are then used to affix upper and lower horizontal portions, respectively, of the mirror 16 to the mounting areas 24,26,28,30.
It is desirable that the parts formed by the injection molding process are uniformly and consistently molded. However, this is difficult to achieve due to the uneven filling of polymer within the mold, especially in relatively large and/or asymmetric parts. Several methods have been utilized to increase the flow of melted plastic so as improve part uniformity and consistency. In one method, higher injection pressures and/or clamping forces are used in order to improve polymer homogeneity. However, this necessitates the use of larger capacity injection molding equipment which increases costs. Other techniques include the use of a hot runner system having heated runners and molds having multiple polymer entrance points. However, these techniques also increase costs since molds incorporating these features are substantially more complicated to fabricate.